The present invention relates to a liquid crystal display device, and more particularly, to an IPS mode liquid crystal display device with excellent viewing angle characteristics and improved brightness.
A display device includes a TFT substrate in which pixels each having a pixel electrode, a thin film transistor (TFT), and the like are arranged in a matrix form. Further, there is provided a counter substrate opposite the TFT substrate, in which color filters, and the like, are formed at positions corresponding to the pixel electrodes of the TFT substrate. Further, a liquid crystal is interposed between the TFT substrate and the counter substrate. Then, an image is formed by controlling the transmittance of light through each pixel by the liquid crystal molecules.
Liquid crystal display devices are flat and lightweight and have been applied in various fields. Small liquid crystal display devices are widely used in mobile phones, digital still cameras (DSC), or other portable devices. The viewing angle characteristics are a problem in the liquid crystal display device. The viewing angle characteristics are a phenomenon that the brightness or the chromaticity varies when the screen is seen from the front and from an oblique angle. The viewing angle characteristics are excellent in the In Plane Switching (IPS) mode that drives liquid crystal molecules by an electric field in the horizontal direction.
Among various types in the IPS mode, for example, there is a mode in which a common electrode is formed in a matted manner and a comb-shaped pixel electrode is provided on the common electrode with an insulating film interposed therebetween, to rotate liquid crystal molecules by the electric field generated between the pixel electrode and the common electrode. This type of mode can increase the transmittance and is currently the mainstream mode. In order to increase the transmittance of a pixel in a liquid crystal display device having the structure described above, there are structures in which the cross-sectional shape of the common electrode is changed, such as those disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2009-150952), Patent Document 2 (Japanese Patent Application Laid-Open No. 2007-86576), and Patent Document 3 (Japanese Patent Application Laid-Open No. 2007-240911). Further, Patent Document 4 (Japanese Patent Application Laid-Open No. 2009-116058) describes a structure in which an opening is provided in the common electrode to adjust the capacity between the pixel electrode and the common electrode.